Friday, December 30, 2011

I was helping a friend debug a OutOfMemory exception in a Java web application. The program made heavy use of StringBuilder and was appending a large number of strings. An entire record set (containing thousands of records) was essentially converted into an XML string.
Strangely when the OOM error occured, there was still plenty of heap memory available. Furthur deep-dive debugging and some googling around, taught a few important lessons.

Whenever the internal buffer capacity of StringBuilder/StringBuffer is exceeded, then the next character array size it creates is twice of the original size. A good blog explaining this is here. Hence it is better to initialize the initial capacity of the StringBuilder to a reasonable value beforehand.

StringBuilder needs a continuous block of memory for further allocation. For e.g. you may have 20MB free heap space, but it may be fragmented. Hence even a 5MB StringBuilder allocation may fail and result in a OOM error. Links to forums - Link 1Link2Link3

Try to use a 64-bit machine, as there are no practical limitations for the heap memory allocation and also it is much easier to find a continous block of memory due to 64-bit addressing.

Alter the design of the program to not store the string in memory, but in a file. Alternatively stream it directly to the HTTP response.

Friday, December 02, 2011

In one of my previous posts, I had blogged about creating a taxonomy of services using functional categorization.
For e.g. Entity Services, Task/Activity Services, Process Services and Infrastructure services.

But services can also be categorized from different perspectives such as layers or intent of use. For e.g.Categorization based on Service Layer:

1. Business Services: Represent high level business functions that define an enterprise.
2. Application Services: Application specific and usually will be aggregated in a composite service at the business level.
3. Infrastructure Services: Utility functions that deliver cross cutting functions.

Categorization based on scope:
1. Enterprise Services: Multiple LOBs use the service.
2. Domain Services: Applicable only within a LOB.
3. Application Services: Local to the App Level.